Is it possible to have one viewer but load a different report source for different users? Say if I have a customer that needs to access one report and another customer access a different one? If so how would I go about doing it?

Yes, on report load, you can load different report base on your paremeter like following code

string reportName="abc.rpt";

DataTable dt=GetFromYourParameterResult();

crRptDoc.Load(Request.PhysicalApplicationPath.ToLower() + reportName);

crRptDoc.Refresh();

crRptDoc.SetDataSource(dt);

crvExploration.DisplayToolbar = true;

crvExploration.DisplayGroupTree = false;

crvExploration.ReportSource = crRptDoc;

crvExploration.DataBind();

ok a small example,,

imagine you are enterng the user name in a textbox, in the coding,

if Textbox1.text="ABC" Then

Rpt.Load(Server.MapPath("ABC.rpt"))

Else IF Textbox1.text="XYZ" Then